Preparation of organic acids



Patented Nov. 6, 1 934 PATENT OFFICE 1,979,450 PREPARATION or ORGANICAoms Gilbert E. Carpenter, Wilmington, DeL, assignor, by mesneassignments, to E. I du Pont de Nemours & Company, Wilmington, DeL, acorporation of Delaware No Drawing. Application February 28, 1931,Serial No. 519,239

18 Claims. (Cl. 260-116) This invention relates to a process for theformation of organic compounds and particularly to the preparation ofmonocarboxylic acids by F the interaction of aliphatic alcohols andcarbon monoxide in the presence of a catalyst.

It is known that organic acids and esters can be prepared by theinteraction, in the vapor or liquid phase, of organic compounds with theoxm ides of carbon. For example, it has been shown that by thecondensation of methyl alcohol with carbon monoxide in the presence of asuitable catalyst, acetic acid, methyl acetate, and methyl formate maybe prepared in proportions which are governed by the particularoperating con- -ditions. Acids have likewise been prepared from methaneand carbon monoxide, from carbon monoxide and water vapor, and fromethers and carbon monoxide. Investigators have experienced nconsiderable diiiiculty in their attemptsto find, -for these reactions,a catalyst which undergiven operating conditions would produce a goodyield of the acid or other compound desired. Some of the catalysts whichhave been suggested ing them and maintaining their initial activity areencountered.

An'object of this invention is to provide a process for the preparationof higher molecular weight organic compounds thru the introduction ofcarbon monoxide into the lower molecular weight organic compounds. Afurther object of this invention is to provide a process for thepreparation of monocarboxylic acids by the condensation ofaliphaticalcohols with carbon oxides in the presence of a catalyst. Anotherobject of this invention is to provide a process forthe preparation ofacids having the structural formulae CsH2n41C0OI-l-from alcohols havingthe structural formulaeCnH2n+1'OI-Iby subjecting the alcohols to theaction of carbon monoxide in the include the hydrogenating and hydratingcata lysts alone or in combination, metal acetate catapresence of apromoted charcoal catalyst. A still further object of this invention isto provide a process for the preparation of acetic acid by theinteraction of methanol and carbon monoxide in the presence of acharcoal catalyst promoted with an inorganic acid and/or an inorganicacid salt. Other objects will hereinafter appear.

According to the present invention organic acids are prepared byinteraction of the aliphatic alcohols and carbon monoxide by passingthese vaporized alcohols together with the carbon monoxide over anactivated charcoal catalyst promoted with the inorganic acids, andinorganic acid salts, such as phosphoric acid, arsenious acid, calciumacid phosphate, etc., or in fact any compound the acidity of which isdue tothe presence of a titratable hydrogen ion. The thus promotedcharcoal catalyst may be supported or not on silica gel, kieselguhr orother-similar inert material.

The charcoal catalyst is not to be confused with inorganic catalystssupported on charcoal. In the latter case the catalytic effect of thecharcoal is negligible due to the fact that its surface has been coatedwith a contiguous covering of the catalytic constituent which alone isacting as the catalyst for, the reaction. On the other hand, when usingcharcoal as a catalyst and promoted in accord with the presentinvention, the charcoal is the dominating influence in the catalyst andthe surface and configuration of the charcoal per se aided by thematerial added as a promoter results in a catalyst which has a muchgreater activity for the alcohol carbon monoxide reaction than, forexample, the same promoting material supported on the charcoal.

The alcohol-carbon monoxide reactions which can be accelerated by theabove described catalysts may be expressed as follows:

The alcohol used may be replaced, if desired, wholly or partlyby thecorresponding alkyl ethers of the alcohol, such as dimethyl ether,diethyl ether, or the mixed alkyl ethers, the alkyl esters,

or other compounds containing one or' more hydrolyzable alkoxy groups.

The synthesis can generally be efliciently carried out under thefollowing operating conditions. The pressure may vary from approximately25 atmospheres to 900 atmospheres or higher with the preferableoperating range in the neighborhood of 350-700 atmospheres. Thetemperature within the reaction zone is quite critical as it determinesto a large extent the product obtained. For example, when themethanol-carbon monoxide reaction is conducted at temperatures below 300C. a low yield of methyl acetate will be obtained. While, on the otherhand, at temperatures above 300 C. the yield of methyl acetate willincrease with a corresponding decrease in the proportion of theparasitic products. 7

The carbon monoxide used may be obtained from various commercialsources, such, for example, as from water gas, producer gas, coke ovengas, and the like, but to obtain products of the highest degree ofpurity it is preferable to remove from such commercial gases theobjectionable constituents such as sulfur compounds, metal carbonyls,etc.

The presence of inert gases in the alcohol-carbon monoxide mixture issometimes desirable. Nitrogen, for instance, has little deleteriousefiect on the reaction or yield and, in fact, may be advantageously usedin order to aid in the temperature control and to prevent too great aconversion of the alcohol and carbon monoxide on one pass through theconversion apparatus. Other strictly inert gases will usually actsimilarly to nitrogen. It is, of course, understood that instead ofintroducing methanol itself into the reaction chamber substances ormixtures of substances which decompose to form alcohols or esters may beemployed, but generally I prefer to introduce methanol directly into thegas stream leading to the converter.

My process can be conveniently carried out by passing purified carbonmonoxide into methanol preferably containing water, maintained at such atemperature that the issuing gases will have the requisite proportion ofmethanol, carbon monoxide and water vapor. I have found that a gaseouscomposition, containing an excess of carbon monoxide over the methanolvapor, will give a good yield of acetic acid and ester on one passthrough a converter containing my catalyst,-the temperature of thereaction chamber being maintained at approximately 300 C. and pressureheld in the neighborhood of 350 atmospheres.

The promoted charcoal catalyst may be prepared by an intimate mixing ofthe desired proportion of the inorganic acid or'inorganic salt with thecharcoal. For example, a finely comminuted activated charcoal is mixedwith 1020% of mono-calcium acid phosphate which is likewise incomminuted form. After a thorough mixing of the two, the resultantcomposition is pilled, in the usual type of pilling machine, and in thatform is ready for catalyzing the reaction. It will be realized that byso preparing the charcoal catalyst there is exposed to the reactantgases a proportion of charcoal surface and of the promoter surfacesubstantially equal to the ratio of these ingredients employed.Alternatively when using a liquid acid as a promoter the reaction may beconducted by mixing the acid, for example, phosphoric acid with methanoland injecting this mixture, together with carbon monoxide, into areaction chamber filled with charcoal. By thus effecting the reactionthe full advantage of the promoting ability of the phosphoric acid onthe charcoal catalyst is realized and an excellent conversion of thereactants to acetic acid results.

Not only can methanol be catalyzed in the presence of carbon monoxideand my catalyst to acetic acid or the condensation product of the aceticacid with methanol, i. e. methyl acetate, but the higher alcohols, suchas ethyl alcohol, propyl alcohol, butyl alcohol, and even the highermolecular weight alcohols, such for example as hexyl alcohol or octylalcohol, may be similarly converted into an acid having correspondinglyone more carbon atom than the alcohol treated. In fact, my process andcatalyst may be employed with any of the monohydric alcohols, providingthese alcohols volatilize without decomposition. When converting thehigher aliphatic alcohols, some of which are not water soluble, andparticularly if water is desired in the reaction, it is preferable tointroduce the alcohol and water into the carbon monoxide as a vapor orspray. Any other suitable procedure may be employed, however, forintimately commingling the vapors of the alcohol and water with theoxide of carbon. When preparing products from the higher molecularweight compounds I may utilize in lieu of the alcohol the ether or esterthereof, the use of which will modify, to some extent, the type ofproduct obtained.

I will now describe a specific embodiment of my process, but it will beunderstood that the details therein given and the compounds employed,either as reactants or catalysts, in no way restrict the scope of thisinvention, but merely illustrate one manner in which my process may becarried out.

Example 1.A gaseous mixture containing 85% carbon monoxide and 5% eachof methanol, water vapor, and hydrogen, is passed over a monocalciumacid phosphate promoted charcoal catalyst prepared as indicated aboveunder a pressure of 700 atmospheres and at a temperature of 300 C. Thecatalyst is disposed in a a suitable chamber for the carrying out ofexothermic gaseous reactions. The condensate obtained upon the coolingof the converted gases contains a high percentage of free acetic acidtogether with some methyl acetate and unconverted methanol.

Example 2.Ethanol is thoroughly mixed with approximately 5% phosphoricacid. The resulting mixture is forced into a reaction chamber containingactivated charcoal wherein it is held at a temperature of 300 C. and apressure of 700 atmospheres. Carbon monoxide is drawn into the chambertogether with water vapor in such amounts that the concentration of thevapors entering the chamber is approximately 85% carbon monoxide, 5%ethanol and phosphoric acid, 5% water, and 5% inert gases. Thecondensate obtained by condensing the vapors issuing from the chambercontain a high percentage of free propionic acid plus propionic esters.

The apparatus, which may be employed for conducting these reactions, maybe of any conventional type and preferably one in which the temperatureof the exothermic reaction can be readily controlled at the optimumvalue. Owing to the corrosive action of acetic acid, the interior of theconverter and apparatus leading therefrom should preferably beprotected. This may be accomplished by using glass or glass-linedapparatus or by plating the inner surfaces thereof with chromium orsilver or using for the conganese, or nickel content. i ,From aconsideration of. the above specification it will be realized that anyprocess in which a carbon oxide is combined with an organic compoundgiving, a product containing a negative radical of an aliphatic acid,and particularly those in iwhich monohydric alcohols are converted tomonocarboxylic acids, will come within the scope of this invention whensuch reactions are accelerated in the presence of a promoted charcoalcatalyst.

I claim:

1. A process for the preparation of aliphatic or ganic acids whichcomprises contacting a compound selected from the group consisting ofmonohydroxy aliphatic alcohols, the alkyl others and the alkyl esters,with an activated charcoal cat alyst promoted with a compoundsubstantially not reducible under the conditions of operation, theacidity of which is due to the presence of a titratable hydrogen ion, inthe presence of carbon i monoxide at reacting temperature.

2. A process for the preparation of aliphatic organic acids whichcomprises contacting an all phatic alcohol which is not substantiallydecomposed when vaporizedwith an activated charcoal not reducible underthe conditions of operation, the acidity of which is due to the presenceof a titratable hydrogen ion, in the presence of carbon monoxide atreacting temperature.

3. A process for the preparation of aliphatic organic acids whichcomprises contacting a monohydroxy aliphatic alcohol which is notsubstantially decomposed when vaporized with a supported activatedcharcoal catalyst promoted with ;a compound substantially not reducibleunder the conditions of operation, the acidity of which is due to thepresence of a titratable hydrogen ion, in the presence of carbonmonoxide at reacting temperature. j 4. A process for the preparation ofacetic acid which comprises contacting methanol with an activatedcharcoal catalyst promoted with a compound substantially not reducibleunder the conditions of operation, the acidity of which is due ,;to thepresence of a titratable hydrogen ion, in the presence of carbonmonoxide at reacting temperature.

5. A process for the preparation of aliphatic organic acids whichcomprises passing carbon monoxide through an aqueous monohydroxyaliphatic alcohol solution and subsequently contacting the resultantvapor at an elevated temperature and pressure with an activated charcoalcatalyst promoted with a compound substantially ,not reducible under theconditions of operation, the acidity of which is due to the presence ofa titratable hydrogen ion.

6. A process for the preparation of aliphatic organic acids whichcomprises adding to a liquid aliphatic alcohol an inorganic acidsubstantially not reducible under the conditions of operation andsubsequently injecting the resulting mixture .,temperature and pressure.

7. A process for the preparation of acetic acid which comprises passingmethanol and carbon monoxide at an elevated temperature and pressureover an activated charcoal catalyst promoted with a compoundsubstantially not reducible unexample, high molybdenum, cobalt,tungsten,chromium, mancatalystpromoted with a compound substantially der theconditi'ons of operation, the acidityuof which is due to the presenceofa titratable hydro-1 gen ion. z l 1 8. A process for the preparationof acetic acid which comprises passing methanol and carbon monoxide atan elevated temperature and press sure over a supported activatedcharcoal catalyst promoted with a compound substantially not reducibleunder the conditions of operation, the

acidity of which is due to the presence of a titratable hydrogen ion.

9. A process for the preparation of acetic acid which comprises passingmethanol and carbon monoxide at an elevated temperature and pressureover an activated charcoal catalyst promoted with monocalcium acidphosphate.

10. A process for the preparation of propionic acid which comprisesadding to an ethanol solution approximately 5% of phosphoric acid andsubsequently injecting the resulting mixture into a reaction chambercontaining activated charcoal.

ll. In a vapor phase process for the preparation of aliphatic organicacids from organic compounds containing at least one hydrolyzable alkoxygroup and carbon monoxide, the steps which comprise adding to a compoundcontaining at least one separate alkoxy group an inorganic acid which issubstantially not reducible under the conditions of operation, andsubsequently injecting the resulting mixture into a reaction chambercontaining activated charcoal.

12. In a vapor phase process for the preparation of aliphatic organicacids from organic compounds containing at least one hydrolyzable alkoxygroup and carbon monoxide, the steps which comprise adding to a compoundcontaining at least one separate alkoxy group an inorganic acid which issubstantially not reducible under the conditions of operation andsubsequently injecting the resulting mixture into a reaction chambercontaining a promoted activated charcoal catalyst.

13. In a process, for the preparation of acetic acid from methanol andcarbon monoxide in the vapor phase, the steps which comprise addingphosphoric acid to methanol. and subsequently injecting the resultingmixture into a reaction chamber containing an activated charcoalcatalyst promoted with phosphoric acid.

14. In a vapor phase process for the preparation of aliphatic organicacids from compounds containing at least one hydrolyzable alkoxy groupand carbon monoxide, the step which comprises efiecting the reaction inthe presence of an activated charcoal catalyst promoted with a compoundof an acidic nature, the acidity of the compound being due to thepresence of a titratable hydrogen ion, and the compound beingsubstantially not reducible under the conditions of operation.

15. A process for the preparation of aliphatic organic acids whichcomprises contacting a compound containing at least one hydrolyzablealkoxy group with an activated charcoal catalyst promoted with acompound substantially non-reducible under the conditions of operation,the acidity of which is due to the presence of a titratable hydrogenion, in the presence of carbon monoxide at reacting temperature.

16. In a process for the preparation of acetic acid from methanol andcarbon monoxide in the vapor phase in the presence of an activatedcharcoal catalyst, the step which comprises preliminarily passing thecarbon monoxide through an aqueous methanol solution.

17. In a process for the preparation of saturated aliphaticmonocarboxylic acids from saturated monohydroxy aliphatic alcohols and.carbon monoxide in the vapor phase in the presence of an activatedcharcoal catalyst, the step which comprises preliminarily passing thecarbon monoxide through an aqueous monohydroxy aliphatic alcoholsolution.

18. In a process for the preparation of aliphatic organicacids fromcompounds containing at least one hydrolyzable alkoxy group and carbonmonoxide in the vapor phase in the presence of an activated charcoalcatalyst, the step which comprises preliminarily passing the carbonmonoxide through an aqueous solution of a compound containing at leastone hydrolyzable alkoxy group.

GILBERT B. CARPENTER.

